Memory Map (x86): Difference between revisions

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→‎"Low" memory (< 1 MiB): update EBDA limit text
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Note: the EBDA is a variable-sized memory area (on different BIOSes). If it exists, it is always immediately below 0xA0000 in memory.
Note: the EBDA is a variable-sized memory area (on different BIOSes). If it exists, it is always immediately below 0xA0000 in memory.
It is absolutely guaranteed to be less than 128 KiB in size. It is often 1 KiB. The biggest ones ever actually seen are 8 KiB.
It is absolutely guaranteed to be at most 128 KiB in size. Older computers typically uses 1 KiB from 0x9FC00 - 0x9FFFF, modern firmware can be found using significantly more.
You can determine the size of the EBDA by using BIOS function [[Detecting Memory (x86)#Detecting Low Memory|INT 12h]], or (often) by examining the word at 0x40E in the BDA (see below).
You can determine the size of the EBDA by using BIOS function [[Detecting Memory (x86)#Detecting Low Memory|INT 12h]], or (often) by examining the word at 0x40E in the BDA (see below).
Both of those methods will tell you the location of the bottom of the EBDA.
Both of those methods will tell you the location of the bottom of the EBDA.
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