Tweaking Optimizing Windows.pdf - GEGeek

CPU level 1 cache
The modern processor is a very fast piece of silicon. Unfortunately, RAM development is so far behind that the processor would be
fatally stalled by the slow memory accesses had it been forced to rely on current RAM technology alone. To alleviate this problem,
designers have integrated a small amount of ultra-fast RAM within the processor core. This small amount of RAM is used to cache
instructions and data for the processor's instantaneous access. Hence, it is known as the primary or level 1 or L1 cache. In current
processor design, the L1 cache can range from 32K to 128KB in size.
Only if the data required is not found in the L1 cache, is the processor required to retrieve it from the L2 cache or the RAM itself.
When it does so, the processor incurs the penalties of accessing much slower memory. Fortunately, the L1 cache is often able to
satisfy the processor's data requirements. In fact, it's so efficient that it makes the entire memory subsystem appear to be almost
as fast as it is. This BIOS feature is used to enable or disable the processor's L1 cache. Naturally, the default and recommended
setting is Enabled.
This feature is useful for overclockers who want to pinpoint the cause of an unsuccessful overclocking attempt. For example, if your
processor cannot reach 1GHz with the L1 cache enabled but can do so when the L1 cache's disabled; then the L1 cache is what's
stopping the processor from running at 1GHz stably. But if the processor still can't reach 1GHz, then the problem lies elsewhere.
However, disabling the L1 cache in order to increase the overclockability of the CPU is a very bad idea. The lack of L1 cache will
cause the processor to stall because the memory subsystem won't be fast enough to continuously feed data to the processor.
Therefore, except for troubleshooting purposes, this feature should be left enabled.
CPU level 2 cache
The modern processor is a very fast piece of silicon. Unfortunately, RAM development is so far behind that the processor would be
fatally stalled by the slow memory accesses had it been forced to rely on current RAM technology alone. To alleviate this problem,
designers have integrated a small amount of ultra-fast RAM within the processor core. This small amount of RAM is used to cache
instructions and data for the processor's instantaneous access. Hence, it is known as the primary or level 1 or L1 cache. In current
processor design, the L1 cache can range from 32K to 128KB in size.
Only if the data required is not found in the L1 cache, is the processor required to retrieve it from the RAM itself. When it does so,
the processor incurs the penalties of accessing much slower memory. Fortunately, the L1 cache is often able to satisfy the
processor's data requirements. In fact, it's so efficient that it makes the entire memory subsystem appear to be almost as fast as it
is.
However, as the disparity between processor speed and RAM speed widens, the penalties incurred whenever there's a L1 cache miss
becomes more significant. This is compounded by the fact that while the size of the L1 cache only doubled or quadrupled in recent
years, the system will often have 16 times to 32 times more RAM! The small L1 cache size is inadequate in most cases and will not
be able to satisfy many of the data requests. If the processor has to retrieve the data directly from the RAM, it will suffer a
significant drop in performance.
As such, designers often include a secondary or level 2 or L2 cache. This cache is designed to meet data requests that the L1 cache
cannot satisfy. Although slower than the L1 cache, the L2 cache compensates by being much larger in size. This allows it to cache a
lot more data compared to the L1 cache. As the two caches working together are able to satisfy over 95% of data reads, the need
to access the much slower RAM is reduced to the minimum. This BIOS feature is used to enable or disable the processor's L2 cache.
Naturally, the default and recommended setting is Enabled.
This feature is useful for overclockers who want to pinpoint the cause of an unsuccessful overclocking attempt. For example, if your
processor cannot reach 1GHz with the L2 cache enabled but can do so when the L2 cache's disabled; then the L2 cache is what's
stopping the processor from running at 1GHz stably. But if the processor still can't reach 1GHz, then the problem lies elsewhere.
However, disabling the L2 cache in order to increase the overclockability of the CPU is a very bad idea. The lack of L2 cache will
cause the processor to stall because the memory subsystem won't be fast enough to continuously feed data to the processor.
Therefore, except for troubleshooting purposes, this feature should be left enabled.
Gate A20 option
The A20 address line is a relic from the past. It came about because the father of x86 processors - the Intel 8088 only had 20
address lines! That meant that it could only address 1MB of memory. When the Intel 80286 processor was introduced, it had 24
address lines. To maintain 100% software compatibility with the 8088, the 80286 had a real mode that would truncate addresses to
20-bits. Unfortunately, a design bug prevented it from truncating the addresses properly. This prevented the 80286 from running
many 8088-compatible software.
To solve this problem, IBM designed an AND gate switch to control the 20th address bit. This switch was henceforth known as the
Gate A20. When enabled, all available address lines would be used by the processor for access to memory above the first
megabyte. In the 8088-compatible real mode, the Gate A20 would be used to clear the 20th bit of all addresses. This allows the
80286 to function like a superfast 8088 processor with access only to the first megabyte of memory. Even in modern systems,
Gate A20 is still important. This is because the processor needs to turn A20 on and off in order to switch between real mode and
protected mode. Since operating systems like Microsoft Windows 98 switch a lot between real mode and protected mode, relying on
the understandably slow keyboard controller is no longer acceptable.
The motherboard chipset's I/O port 0x92 (System Control Port A) was therefore recruited to take over the job. A lot faster than the
keyboard controller, the 0x92 port allows the processor to switch much faster between real mode and protected mode. This
translates into faster memory access and better system performance. This BIOS feature is used to determine the method by which
Gate A20 is controlled. The Normal option forces the chipset to use the slow keyboard controller to do the switching. The Fast
option, on the other hand, allows the chipset to use its own 0x92 port for faster switching. No candy for guessing which is the
recommended setting!
Please note this feature is only important for operating systems that switch a lot between real mode and protected mode. These
operating systems include 16-bit operating systems like MS-DOS and 16-bit/32-bit hybrid operating systems like Microsoft Windows
98. This feature has no effect if the operating system only runs in real mode (no operating system currently in use does that, as far
as I know) or if the operating system operates entirely in protected mode (i.e. Microsoft Windows XP). This is because if no A20