VIJAYBHASKAR GUDIBOINA ID 10000125667
3.6 A 32-bit processor can address 4G memory. How do you build a 32-bit computer with more than 4G memory? A 32-bit only CPU can address a maximum of 4GB (2^32 bits = 4294967296 bits = 4194304 KB = 4096 MB = 4GB). This is the limitation of 32-bit systems. Allocating a page file on top of your RAM if you already have 4GB of physical RAM will be useless. However, even if you have 4GB of physical RAM installed you won't be able to use all of it for your applications. A portion of the upper 3GB address is being occupied by your system devices like your graphics card, BIOS, PCI, etc. That's why on some systems, you will see only 3.27GB of available RAM. This usually varies depending on the hardware. Take a look at the crude illustration below.
In normal mode, the 32-bit OS can address this much:
+---------------+ 4GB
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+ 0
Now if you put in your stuff and your RAM, say 2GB, in this address space:
+---------------+ 4GB
| BIOS, PCI |
| GFX, ETC... |
| |
| |
|---------------+ 3 GB
| |
| |
| EMPTY |
| |
|---------------+ 2 GB
| |
| RAM |
| |
| |
+---------------+ 0

If you put another 1GB RAM in there for a total of 3GB it will still be fine because you still have 1GB of EMPTY space.
But if you put another gig (so you now have a total of 4), then you have an overlap. Part of the last GB will be hidden behind BIOS, PCI, GFX, etc. so Windows cannot give it an address, and it will be "lost". Memory remapping can solve it by moving the last gig above PCI, GFX, BIOS, etc. but then you'll need an OS that can go beyond 4GB, which a 32-bit OS cannot do, and that's where the 64-bit OS comes to the rescue. Unfortunately, if you only have a 32-bit CPU, you can't install a 64-bit OS.

Meanwhile, having a 64-bit OS doesn't always mean you can address 2^64 bits of memory. While the maximum RAM limit for 32-bit Windows 7 editions is 4GB, when it comes to the 64-bit editions, the amount of memory that the OS can address depends on which edition you are running.

Here are the upper RAM limits for the different editions of Windows 7:
Starter: 8GB
Home Basic: 8GB
Home Premium: 16GB
Professional: 192GB
Enterprise: 192GB
Ultimate: 192GB A 32-bit only CPU can address a maximum of 4GB (2^32 bits = 4294967296 bits = 4194304 KB = 4096 MB = 4GB). This is the limitation of 32-bit systems. Allocating a page file on top of your RAM if you already have 4GB of physical RAM will be useless.
However, even if you have 4GB of physical RAM installed you won't be able to use all of it for your applications. A portion of the upper 3GB address is being occupied by your system devices like your graphics card, BIOS, PCI, etc. That's why on some systems, you will see only 3.27GB of available RAM. This usually varies depending on the hardware. Take a look at the crude illustration below.
In normal mode, the 32-bit OS can address this much:
+---------------+ 4GB
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+ 0

Now if you put in your stuff and your RAM, say 2GB, in this address space:

+---------------+ 4GB
| BIOS, PCI |
| GFX, ETC... |
| |
| |
|---------------+ 3 GB
| |
| |
| EMPTY |
| |
|---------------+ 2 GB
| |
| RAM |
| |
| |
+---------------+ 0

If you put another 1GB RAM in there for a total of 3GB it will still be fine because you still have 1GB of EMPTY space.

But if you put another gig (so you now have a total of 4), then you have an overlap. Part of the last GB will be hidden behind BIOS, PCI, GFX, etc. so Windows cannot give it an address, and it will be "lost".

Memory remapping can solve it by moving the last gig above PCI, GFX, BIOS, etc. but then you'll need an OS that can go beyond 4GB, which a 32-bit OS cannot do, and that's where the 64-bit OS comes to the rescue. Unfortunately, if you only have a 32-bit CPU, you can't install a 64-bit OS.

Meanwhile, having a 64-bit OS doesn't always mean you can address 2^64 bits of memory. While the maximum RAM limit for 32-bit Windows 7 editions is 4GB, when it comes to the 64-bit editions, the amount of memory that the OS can address depends on which edition you are running.

Here are the upper RAM limits for the different editions of Windows 7:

Starter: 8GB
Home Basic: 8GB
Home Premium: 16GB
Professional: 192GB
Enterprise: 192GB
Ultimate: 192GB
3.7 What are the similarities between cache memory and virtual memory? The similarity of cache memory and virtual memory in their purpose of being “proxy” memory, to assist RAM in processing data. Another is when cache is used in software mode (such as in an Internet browsers), it is variable in size. You can set the size of cache (for programs that allow it, like Internet Explorer) and virtual memory as well. They are also both memories that cannot be directly accessed by the user while in operation (though you can look in the Internet cache in Windows when nothing is loading. CPU and main board cache and the Windows swap file are definitely inaccessible). Software-based Cache and virtual memory also use hard disk space. In one source below, virtual memory is even considered a form of caching. Of course, in both kinds of memory, data is handled in organized chunks before being processed all the way through. The cache is a small amount of fast memory that sits between the processor and memory to bridge the speed gap between the CPU and main memory .Like cache memory, virtual memory is a transition between main memory and the disk storage.

3.10 What are the benefits of using memory segmentation technique? Segmentation is a technique which divides memory into logically related data units * Module, procedure, stack, data, files, etc. * Virtual addresses become <segment #, offset> * Units of memory from user’s perspective Segmentation is only allowed for sharing program code among users.
The shared segment contains:
An area where unchangeable code (Re-entrant code) is stored.
Several data areas, one for each user.
Users share the code, which cannot be modified, and can modify the information stored in their own data areas as needed without affecting the data stored in other users’ data areas.
Use segments to manage logically related units * Module, procedure, stack, file, data, etc. * Segments vary in size, but usually large (multiple pages)
 Use pages to partition segments into fixed size chunks * Makes segments easier to manage within physical memory Segments become “page able” – rather than moving segments
Into and out of memory, just move page portions of segment * Need to allocate page table entries only for those pieces of the segments that have themselves been allocated