Understanding Hard Drive Space

Understanding Hard Drive Space


The hard drive space on any computer with the Microsoft® Windows® operating system preinstalled may appear to be smaller than the size stated in the product specifications, in the documentation, or on the box. Hard drives are described and advertised by manufacturers in terms of decimal (base 10) capacity.

Microsoft Windows and other programs, such as FDISK, use the binary (base 2) numbering system.

In decimal notation, one megabyte (MB) is equal to 1,000,000 bytes, and one gigabyte (GB) is equal to 1,000,000,000 bytes.

In the binary numbering system which computers use,

1 bit = a single digit, either 1 or 0

8 bits = 1 byte, a combination of 1’s and 0’s

1024 Bytes = 1 KB (kilobyte)

1024 Kilobytes = 1 MB (megabyte)

1024 Megabytes = 1 GB (gigabyte)

Because of the different measuring systems, you may see a difference between the size reported by Microsoft® Windows® and the size advertised. The storage capacity of the hard drive is as advertised.

For example Advertised — Actual Capacity
10GB — ~9.31 GB
20GB — ~18.63 GB
30GB — ~27.94 GB
40GB — ~37.25 GB
60GB — ~55.88 GB
80GB — ~74.51 GB
100GB — ~93.13 GB
120GB — ~111.76 GB
160GB — ~149.01 GB
180GB — ~167.64 GB
200GB — ~186.26 GB
250GB — ~232.83 GB
320GB — ~298.02 GB
400GB — ~372.53 GB
500GB — ~465.66 GB
750GB — ~698.49 GB
1TB — ~931.32GB

Microsoft® Windows® reports smaller capacity in the Windows Explorer tool and in the computer window because it shows information about one partition on the hard disk drive at a time. One of the partitions could also contain a System Recovery partition.

Bits, Bytes, Kilobytes, Megabytes, Gigabytes Explained In Plain English http://tandemtables.com/database/tables/basics/BYTES_EASY.html


Note about systems configured with 4 GB of memory. For computers with a 32 bit operating system, all memory above 3 GB may not be available because of system resource requirements.

This limitation is not limited by various vendor systems. The memory above 3 GB is used for system resources.

Refer to this link for additional information.

Physical Memory/RAM Limits: Windows 10

The following table specifies the limits on physical memory for Windows 10. There are differences for earlier systems such as Windows XP, Vista, Windows 7 & 8.


X86 = 32Bit Operating system X64 = 64Bit Operating system

VersionLimit on X86Limit on X64
Windows 10 Enterprise4 GB2TB
Windows 10 Education4 GB2TB
Windows 10 Pro4 GB2TB
Windows 10 Home4 GB128GB

Although the figures above set the memory/RAM limits for

Microsoft® Windows® theses can and are further limited by

manufacturers of *motherboards and the type of processor

(CPU), supported by that motherboard.


*A motherboard (sometimes alternatively known as the mainboard, system board, baseboard, planar board or logic board, or colloquially, a mobo) is the main printed circuit board (PCB) found in general purpose microcomputers and other expandable systems.