**Q. **Presume that we agree that 1 kilobyte is 1,024 bytes 1 megabyte is 1,0242 bytes and 1 gigabyte is 1,0243 bytes. This progression carries on through terabytes, petabytes, and exabytes (1, 0246). There are at present several new proposed scientific projects that plan to record and store a few Exabyte's of data during the next decade. To answer the subsequent questions you will require making a few reasonable assumptions stating the assumptions that you make.

a. How many disk drives would be necessary to hold 4 Exabyte of data?

b. How many magnetic tapes would be necessary to hold 4 Exabyte of data?

c. How many optical tapes would be necessary to hold 4 Exabyte of data (see Exercise 12.21)?

d. How several holographic storage cartridges would be required to hold 4 Exabyte of data (see Exercise 12.20)?

e. How many cubic feet of storage space would every option require?

**Answer:**

a. Assume that a disk drive holds 10 GB. Then 100 disks hold 1 TB, 100,000 disks hold 1 PB, and 100,000,000 disks hold 1 EB. To store 4 EB would need about 400 million disks. If a magnetic tape holds 40 GB only 100 million tapes would be required. If an optical tape embraces 50 times more data than a magnetic tape 2 million optical tapes would suffice. If a holographic cartridge is able to store 180 GB about 22.2 million cartridges would be required.

b. A 3.5" disk drive is about 1" high 4" wide as well as 6" deep. In feet this is 1/12 by 1/3 by 1/2 or else 1/72 cubic feet. Packed densely the 400 million disks would inhabit 5.6 million cubic feet. If we permit a factor of two for air space and space for power supplies the required capacity is about 11 million cubic feet.

c. A 1/2" tape cartridge is around 1" high and 4.5" square. The volume is around 1/85 cubic feet. For 100 million magnetic tapes the packed densely the volume is about 1.2 million cubic feet. For 2 million optical tapes the volume is 23,400 cubic feet.

d. A CD-ROM is 4.75" in diameter in addition to about 1/16" thick. If we presume that a holo store disk is stored in a library slot that is 5" square and 1/8" wide we compute the volume of 22.2 million disks to be about 40000 cubic feet.