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BIOS Option Of The Week
Since 1999, we have been developing the BIOS Optimization Guide, affectionately known as the BOG. From a meager beginning of a single page, it now covers over 440 BIOS options. As old BOG readers will know, we started offering two editions of the BOG since Revision 8.0 - a simplified edition and the complete edition.
In the simplified edition, the description of each BIOS option in this guide is condensed and written in a simplified format. This simplified edition is not a sampler or demo version of the complete BIOS Optimization Guide. It is merely a simplified version with all the essential points and minus the frills.
The complete edition, on the other hand, features both simplified descriptions as well as full details of each BIOS option. This allows you to quickly get the gist of what each BIOS option mean and delve deeper into the details if you wish to learn more about it.
Normally, the complete edition is only available to subscribers who help sponsor the development of the guide through a small fee. However, that changes today! From now on, we will post a BIOS option from the complete edition of the BIOS Optimization Guide every weekend. We hope this will help you improve your knowledge of BIOS options. If you find the guide useful, be sure to tell your friends! 
This week, we will be taking a look at the ISA Shared Memory BIOS option.
ISA Shared Memory
Common Options : 64KB, 32KB, 16KB, Disabled
Quick Review
This is an ISA-specific BIOS option. In motherboards that have ISA slots, the BIOS can be set to reserve part of the upper memory area (UMA), which resides between 640 KB and 1 MB, for use by ISA expansion cards. This is particularly important for older operating systems like MS-DOS because it frees up conventional memory (the first 640 KB) for use by the operating system and applications.
If your ISA expansion card requires an upper memory area of 64 KB in size, select the 64KB option. Similarly, if it requires just 32 KB or 16 KB of upper memory, select the 32KB or 16KB options respectively.
If you are not sure how much memory your ISA expansion card requires, select 64KB. It will work with cards that only require 32 KB or 16 KB of upper memory. The rest of the reserved upper memory area will be left unused.
If you do not have any ISA expansion cards installed, leave it at its default setting of Disabled. This frees up the UMA for use by the operating system (or third-party memory managers) to store TSR (Terminate and Stay Resident) programs.
Details
This is an ISA-specific BIOS option. In motherboards that have ISA slots, the BIOS can be set to reserve part of the upper memory area (UMA), which resides between 640 KB and 1 MB, for use by ISA expansion cards. This is particularly important for older operating systems like MS-DOS because it frees up conventional memory (the first 640 KB) for use by the operating system and applications.
In truly old motherboards with multiple ISA slots, you will have the option to set both the memory address range and the reserved memory size. You may have to set jumpers on your ISA expansion cards to prevent two or more cards using the same memory address range, but this allows you to reserve segments of the upper memory area for your ISA expansion cards.
"Newer" PCI-based motherboards have no need for so many ISA slots. Most, if not all, only have a single ISA slot for the rare ISA expansion card that had not yet been "ported" to the PCI bus. Therefore, their BIOS only has a single BIOS option, which allows you to set the size of the UMA to be reserved for the single ISA card. There's no need to set the memory address range because there is only one ISA slot, so you need not worry about conflicts between multiple ISA cards. All you need to do is set the reserved memory size.
To do so, you will have to find out how much memory your ISA expansion card requires. Check the manual that came with the card. It ranges from 16 KB to 64 KB. Once you know how much upper memory your ISA expansion card requires, use this BIOS setting to reserve the memory segment for your card.
If your ISA expansion card requires an upper memory area of 64 KB in size, select the 64KB option. Similarly, if it requires just 32 KB or 16 KB of upper memory, select the 32KB or 16KB options respectively.
If you are not sure how much memory your ISA expansion card requires, select 64KB. It will work with cards that only require 32 KB or 16 KB of upper memory. The rest of the reserved upper memory area will be left unused.
If you do not have any ISA expansion cards installed, leave it at its default setting of Disabled. This frees up the UMA for use by the operating system (or third-party memory managers) to store TSR (Terminate and Stay Resident) programs.
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| Date | Revision | Revision History |
| 01-12-2008 | 1.0 | Covered the Intel Turbo Mode Tech BIOS option. |
| 07-12-2008 | 1.1 | Covered the DRDY Timing BIOS option. |
| 14-12-2008 | 1.2 | Covered the ACPI 2.0 Support BIOS option. |
| 21-12-2008 | 1.3 | Covered the Overclock Recovery BIOS option. |
| 28-12-2008 | 1.4 | Covered the EXT-P2P's Discard Time BIOS option. |
| 04-01-2009 | 1.5 | Covered the Graphics Aperture Size BIOS option. |
| 11-01-2009 | 1.6 | Covered the Memory DQ Drive Strength BIOS option. |
| 18-01-2009 | 1.7 | Covered the PCI-E Maximum Payload Size BIOS option. |
| 25-01-2009 | 1.8 | Covered the Max Async Latency BIOS option. |
| 01-02-2009 | 1.9 | Covered the Chipkill BIOS option. |
| 08-02-2009 | 2.0 | Covered the PCI Delay Transaction BIOS option. |
| 15-02-2009 | 2.1 | Covered the MAC Media Interface BIOS option. |
| 22-02-2009 | 2.2 | Covered the Digital Locked Loop (DLL) BIOS option. |
| 01-03-2009 | 2.3 | Covered the PCI-E Max Read Request Size BIOS option. |
| 08-03-2009 | 2.4 | Covered the DBI Output for AGP Trans. BIOS option. |
| 15-03-2009 | 2.5 | Covered the V-Link Mode Selection BIOS option. |
| 21-03-2009 | 2.6 | Covered the Errata 94 Enhancement BIOS option. |
| 28-03-2009 | 2.7 | Covered the Errata 123 Enhancement BIOS option. |
| 05-04-2009 | 2.8 | Covered the Dynamic Idle Cycle Counter BIOS option. |
| 11-04-2009 | 2.9 | Covered the Gate A20 Option BIOS option. |
| 20-04-2009 | 3.0 | Covered the Split Lock Operations BIOS option. |
| 26-04-2009 | 3.1 | Covered the DOS Flat Mode BIOS option. |
| 03-05-2009 | 3.2 | Covered the FPU OPCODE Compatible Mode BIOS option. |
| 10-05-2009 | 3.3 | Covered the LD-Off Dram RD/WR Cycles BIOS option. |
| 17-05-2009 | 3.4 | Covered the Odd Divisor Correct BIOS option. |
| 24-05-2009 | 3.5 | Covered the No-Execute Memory Protect BIOS option. |
| 31-05-2009 | 3.6 | Covered the ISA Enable Bit BIOS option. |
| 07-06-2009 | 3.7 | Covered the Interrupt 19 Capture BIOS option. |
| 14-06-2009 | 3.8 | Covered the Internal Graphics Mode Select BIOS option. |
| 28-06-2009 | 3.9 | Covered the PCI 2.1 Compliance BIOS option. |
| 05-07-2009 | 4.0 | Covered the SATA AHCI Mode BIOS option. |
| 12-07-2009 | 4.1 | Covered the L1 Data Cache Context Mode BIOS option. |
| 09-08-2009 | 4.2 | Covered the Maximum Read Request Size BIOS option. |
| 16-08-2009 | 4.3 | Covered the Delay DRAM Read Latch BIOS option. |
| 23-08-2009 | 4.4 | Covered the No Mask of SBA FE BIOS option. |
| 29-08-2009 | 4.5 | Covered the CPU Fast String BIOS option. |
| 06-09-2009 | 4.6 | Covered the CPUID Maximum Value Limit BIOS option. |
| 19-09-2009 | 4.7 | Covered the CPU Hardware Prefetch BIOS option. |
| 27-09-2009 | 4.8 | Covered the CPU/DRAM CLK Synch CTL BIOS option. |
| 04-10-2009 | 4.9 | Covered the CPU Drive Strength BIOS option. |
| 18-10-2009 | 5.0 | Covered the CPU Direct Access FB BIOS option. |
| 24-10-2009 | 5.1 | Covered the CPU Adjacent Sector Prefetch BIOS option. |
| 01-11-2009 | 5.2 | Covered the Compatible FPU OPCODE BIOS option. |
| 08-11-2009 | 5.3 | Covered the Clock Throttle BIOS option. |
| 15-11-2009 | 5.4 | Covered the Byte Merge BIOS option. |
| 21-11-2009 | 5.5 | Covered the Burn-In Mode BIOS option. |
| 29-11-2009 | 5.6 | Covered the Boot To OS/2 BIOS option. |
| 06-12-2009 | 5.7 | Covered the Boot Up Floppy Seek BIOS option. |
| 13-12-2009 | 5.8 | Covered the Auto Turn Off PCI Clock Pin BIOS option. |
| 20-12-2009 | 5.9 | Covered the Athlon 4 SSED Instruction BIOS option. |
| 27-12-2009 | 6.0 | Covered the ATA(PI) 80-Pin Cable Detection BIOS option. |
| 02-01-2010 | 6.1 | Covered the AT Bus Clock BIOS option. |
| 17-01-2010 | 6.2 | Covered the Assign IRQ For VGA BIOS option. |
| 24-01-2010 | 6.3 | Covered the ASF Support BIOS option. |
| 31-01-2010 | 6.4 | Covered the APIC Function BIOS option. |
| 07-02-2010 | 6.5 | Covered the Anti-Virus Protection BIOS option. |
| 14-02-2010 | 6.6 | Covered the Anti-Dot Crawl BIOS option. |
| 21-02-2010 | 6.7 | Covered the AGPCLK / CPUCLK BIOS option. |
| 07-03-2010 | 6.8 | Covered the AGP to DRAM Prefetch BIOS option. |
| 14-03-2010 | 6.9 | Covered the AGP Secondary Lat Timer BIOS option. |
| 21-03-2010 | 7.0 | Covered the AGP Read Synchronization BIOS option. |
| 11-04-2010 | 7.1 | Covered the AGP Prefetch BIOS option. |
| 01-05-2010 | 7.2 | Covered the AGP Performance Control BIOS option. |
| 09-05-2010 | 7.3 | Covered the AGP/PCI Burn-in Mode BIOS option. |
| 16-05-2010 | 7.4 | Covered the AGP ISA Aliasing BIOS option. |
| 23-05-2010 | 7.5 | Covered the AGP Driving Value BIOS option. |
| 30-05-2010 | 7.6 | Covered the AGP Driving Control BIOS option. |
| 06-06-2010 | 7.7 | Covered the AGP Drive Strength BIOS option. |
| 13-06-2010 | 7.8 | Covered the AGP Always Compensate BIOS option. |
| 21-06-2010 | 7.9 | Covered the AGP 3.0 Calibration Cycle BIOS option. |
| 27-06-2010 | 8.0 | Covered the Adjacent Cache Line Prefetch BIOS option. |
| 04-07-2010 | 8.1 | Covered the ACPI SRAT Table BIOS option. |
| 11-07-2010 | 8.2 | Covered the Act Bank A to B CMD Delay BIOS option. |
| 18-07-2010 | 8.3 | Covered the ACPI APIC Function BIOS option. |
| 25-07-2010 | 8.4 | Covered the 2T Command BIOS option. |
| 31-07-2010 | 8.5 | Covered the XD Technology BIOS option. |
| 08-08-2010 | 8.6 | Covered the Write Recovery Time BIOS option. |
| 15-08-2010 | 8.7 | Covered the Write Data In to Read Delay BIOS option. |
| 29-08-2010 | 8.8 | Covered the Write CAS Latency (Twcl) BIOS option. |
| 05-09-2010 | 8.9 | Covered the Watchdog Timer BIOS option. |
| 12-09-2010 | 9.0 | Covered the Watch Dog Timer Select BIOS option. |
| 26-09-2010 | 9.1 | Covered the Video RAM Cacheable BIOS option. |
| 10-10-2010 | 9.2 | Covered the Video Memory Cache Mode BIOS option. |
| 17-10-2010 | 9.3 | Covered the Video BIOS Shadowing BIOS option. |
| 24-10-2010 | 9.4 | Covered the Video BIOS Cacheable BIOS option. |
| 31-10-2010 | 9.5 | Covered the VGA Share Memory Size BIOS option. |
| 07-11-2010 | 9.6 | Covered the USWC Write Posting BIOS option. |
| 14-11-2010 | 9.7 | Covered the USB Port 64/60 Emulation BIOS option. |
| 20-11-2010 | 9.8 | Covered the System BIOS Cacheable BIOS option. |
| 05-12-2010 | 9.9 | Covered the Synchronous Mode Select BIOS option. |
| 12-12-2010 | 10.0 | Covered the Suppress Unused PCI Slot Clocks BIOS option. |
| 19-12-2010 | 10.1 | Covered the SuperStability Mode BIOS option. |
| 09-01-2011 | 10.2 | Covered the SM I/O Buffers Control BIOS option. |
| 15-01-2011 | 10.3 | Covered the Share Memory Size BIOS option. |
| 22-01-2011 | 10.4 | Covered the Search for MDA Resources BIOS option. |
| 30-01-2011 | 10.5 | Covered the SDRAM Write to Read Command Delay BIOS option. |
| 05-02-2011 | 10.6 | Covered the SDRAM Write Recovery Time BIOS option. |
| 13-02-2011 | 10.7 | Covered the SDRAM Trrd Timing Value BIOS option. |
| 20-02-2011 | 10.8 | Covered the SDRAM Leadoff Command BIOS option. |
| 26-02-2011 | 10.9 | Covered the SDRAM RAS Pulse Width BIOS option. |
| 06-03-2011 | 11.0 | Covered the SDRAM RAS-to-CAS Delay BIOS option. |
| 13-03-2011 | 11.1 | Covered the SDRAM RAS Precharge Time BIOS option. |
| 03-04-2011 | 11.2 | Covered the SDRAM PH Limit BIOS option. |
| 10-04-2011 | 11.3 | Covered the SDRAM Page Closing Policy BIOS option. |
| 17-04-2011 | 11.4 | Covered the SDRAM Bank Interleave BIOS option. |
| 24-04-2011 | 11.5 | Covered the SDRAM Burst Length BIOS option. |
| 01-05-2011 | 11.6 | Covered the SDRAM RAS Precharge Delay BIOS option. |
| 15-05-2011 | 11.7 | Covered the SDRAM ECC Setting BIOS option. |
| 22-05-2011 | 11.8 | Covered the SDRAM Active to Precharge Delay BIOS option. |
| 29-05-2011 | 11.9 | Covered the SDRAM Bank-to-Bank Delay BIOS option. |
| 05-06-2011 | 12.0 | Covered the SDRAM Command Leadoff Time BIOS option. |
| 11-06-2011 | 12.1 | Covered the SDRAM Row Cycle Time BIOS option. |
| 25-06-2011 | 12.2 | Covered the SDRAM CAS Latency Time BIOS option. |
| 03-07-2011 | 12.3 | Covered the TM2 Bus VID BIOS option. |
| 10-07-2011 | 12.4 | Covered the Virtualization BIOS option. |
| 17-07-2011 | 12.5 | Covered the Vanderpool Technology BIOS option. |
| 24-07-2011 | 12.6 | Covered the V-Link 8X Support BIOS option. |
| 31-07-2011 | 12.7 | Covered the V-Link Mode Selection BIOS option. |
| 07-08-2011 | 12.8 | Covered the USB Mass Storage Reset Delay BIOS option. |
| 14-08-2011 | 12.9 | Covered the TV Standard BIOS option. |
| 21-08-2011 | 13.0 | Covered the SSE/SSE2 Instructions BIOS option. |
| 28-08-2011 | 13.1 | Covered the S2K Bus Driving Strength BIOS option. |
| 11-09-2011 | 13.2 | Covered the PCI Bus Parking BIOS option. |
| 18-09-2011 | 13.3 | Covered the PIRQ x Use IRQ No. BIOS option. |
| 25-09-2011 | 13.4 | Covered the On-Chip Frame Buffer Size BIOS option. |
| 02-10-2011 | 13.5 | Covered the Refresh Mode Select BIOS option. |
| 09-10-2011 | 13.6 | Covered the PEG/Onchip VGA Control BIOS option. |
| 16-10-2011 | 13.7 | Covered the PCI Clock Synchronization Mode BIOS option. |
| 23-10-2011 | 13.8 | Covered the MPS Control Version For OS BIOS option. |
| 30-10-2011 | 13.9 | Covered the Split Lock Operations BIOS option. |
| 06-11-2011 | 14.0 | Covered the Intel Dynamic Acceleration BIOS option. |
| 12-11-2011 | 14.1 | Covered the CPU On-Die Termination BIOS option. |
| 27-11-2011 | 14.2 | Covered the DBI Output for AGP Trans. BIOS option. |
| 11-12-2011 | 14.3 | Covered the Node Memory Interleave BIOS option. |
| 18-12-2011 | 14.4 | Covered the DRAM Ratio H/W Strap BIOS option. |
| 25-12-2011 | 14.5 | Covered the ARMD Emulation Type BIOS option. |
| 01-01-2012 | 14.6 | Covered the Interrupt 19 Capture BIOS option. |
| 08-01-2012 | 14.7 | Covered the Reserved Memory Size BIOS option. |
| 15-01-2012 | 14.8 | Covered the PCI Dynamic Bursting BIOS option. |
| 29-01-2012 | 14.9 | Covered the PSB Parking BIOS option. |
| 05-02-2012 | 15.0 | Covered the PCI Express Burn-in Mode BIOS option. |
| 12-02-2012 | 15.1 | Covered the PCI/VGA Palette Snoop BIOS option. |
| 19-02-2012 | 15.2 | Covered the Bypass Max BIOS option. |
| 25-02-2012 | 15.3 | Covered the DCLK Feedback Delay BIOS option. |
| 04-03-2012 | 15.4 | Covered the DVMT/FIXED Memory BIOS option. |
| 11-03-2012 | 15.5 | Covered the NX Technology BIOS option. |
| 17-03-2012 | 15.6 | Covered the Odd Divisor Correct BIOS option. |
| 01-04-2012 | 15.7 | Covered the FIXED Memory Size BIOS option. |
| 08-04-2012 | 15.8 | Covered the Delay DRAM Read Latch BIOS option. |
| 15-04-2012 | 15.9 | Covered the PCI Master Read Caching BIOS option. |
| 22-04-2012 | 16.0 | Covered the Bank Swizzle Mode BIOS option. |
| 29-04-2012 | 16.1 | Covered the Digital Locked Loop (DLL) BIOS option. |
| 06-05-2012 | 16.2 | Covered the Internal Graphics Mode Select BIOS option. |
| 13-05-2012 | 16.3 | Covered the CPU Direct Access FB BIOS option. |
| 20-05-2012 | 16.4 | Covered the DRDY Timing BIOS option. |
| 27-05-2012 | 16.5 | Covered the Asynclat BIOS option. |
| 03-06-2012 | 16.6 | Covered the DCQ Bypass Maximum BIOS option. |
| 10-06-2012 | 16.7 | Covered the CPU Hardware Prefetch BIOS option. |
| 16-06-2012 | 16.8 | Covered the CPU Thermal-Throttling BIOS option. |
| 23-06-2012 | 16.9 | Covered the CPU Differential Amplitude BIOS option. |
| 30-06-2012 | 17.0 | Covered the CPU Latency Timer BIOS option. |
| 08-07-2012 | 17.1 | Covered the CPU to PCI Post Write BIOS option. |
| 15-07-2012 | 17.2 | Covered the CPU to PCI Write Buffer BIOS option. |
| 22-07-2012 | 17.3 | Covered the CPU Adjacent Sector Prefetch BIOS option. |
| 28-07-2012 | 17.4 | Covered the Display Card Priority BIOS option. |
| 04-08-2012 | 17.5 | Covered the DVMT Mode BIOS option. |
| 12-08-2012 | 17.6 | Covered the NVIDIA GPU Ex BIOS option. |
| 19-08-2012 | 17.7 | Covered the PCI Master Bus TimeOut Control BIOS option. |
| 26-08-2012 | 17.8 | Covered the Graphic Win Size BIOS option. |
| 02-09-2012 | 17.9 | Covered the Graphic Window WR Combin BIOS option. |
| 09-09-2012 | 18.0 | Covered the Frame Buffer Size BIOS option. |
| 16-09-2012 | 18.1 | Covered the PEG Port VC1/Map BIOS option. |
| 23-09-2012 | 18.2 | Covered the No Mask of SBA FE BIOS option. |
| 29-09-2012 | 18.3 | Covered the L2 Streaming Prefetch BIOS option. |
| 07-10-2012 | 18.4 | Covered the DOS Flat Mode BIOS option. |
| 13-10-2012 | 18.5 | Covered the Byte Merge BIOS option. |
| 21-10-2012 | 18.6 | Covered the Chipkill BIOS option. |
| 26-10-2012 | 18.7 | Covered the K7 CLK_CTL Select BIOS option. |
| 04-11-2012 | 18.8 | Covered the FPU OPCODE Compatible Mode BIOS option. |
| 11-11-2012 | 18.9 | Covered the CPUID Maximum Value Limit BIOS option. |
| 18-11-2012 | 19.0 | Covered the ISA Enable Bit BIOS option. |
| 25-11-2012 | 19.1 | Covered the DQS Training Control BIOS option. |
| 02-12-2012 | 19.2 | Covered the DRAM Read Latch Delay BIOS option. |
| 08-12-2012 | 19.3 | Covered the DRAM Burst Length 8QW BIOS option. |
| 16-12-2012 | 19.4 | Covered the DRAM Ratio (CPU:DRAM) BIOS option. |
| 23-12-2012 | 19.5 | Covered the PreChrg to Act CMD BIOS option. |
| 30-12-2012 | 19.6 | Covered the DRAM Data Integrity Mode BIOS option. |
| 06-01-2013 | 19.7 | Covered the SDRAM Idle Limit BIOS option. |
| 13-01-2013 | 19.8 | Covered the DRAM Idle Timer BIOS option. |
| 20-01-2013 | 19.9 | Covered the SDRAM Row Active Time BIOS option. |
| 03-02-2013 | 20.0 | Covered the DRAM Act to PreChrg CMD BIOS option. |
| 17-02-2013 | 20.1 | Covered the SDRAM 1T Command BIOS option. |
| 24-02-2013 | 20.2 | Covered the SDRAM Cycle Length BIOS option. |
| 03-03-2013 | 20.3 | Covered the No-Execute Memory Protect BIOS option. |
| 10-03-2013 | 20.4 | Covered the Refressh Interval BIOS option. |
| 17-03-2013 | 20.5 | Covered the SDRAM Tras Timing Value BIOS option. |
| 24-03-2013 | 20.6 | Covered the SDRAM Trc Timing Value BIOS option. |
| 31-03-2013 | 20.7 | Covered the R/W Queue Bypass BIOS option. |
| 07-04-2013 | 20.8 | Covered the SDRAM Page Hit Limit BIOS option. |
| 14-04-2013 | 20.9 | Covered the OS Select For DRAM > 64MB BIOS option. |
| 21-04-2013 | 21.0 | Covered the SDRAM 1T Command Control BIOS option. |
| 27-04-2013 | 21.1 | Covered the DRAM Page-Mode BIOS option. |
| 07-05-2013 | 21.2 | Covered the Passive Release BIOS option. |
| 12-05-2013 | 21.3 | Covered the HPET Support BIOS option. |
| 19-05-2013 | 21.4 | Covered the ISA Shared Memory BIOS option. |
