• suppose the daytime processing load consists of 60% CPU activity and 40% disk activity. Your customers are complaining that the system is slow. After doing some research, you have learned that you can upgrade your disks for $8,000 to make them 2.5 times as fast as they are currently. You have also learned that you can upgrade your CPU to make it 1.4 as fast for $5,000. 

how would you answer exercise 8 if the system activity consists of 55% processor time and 45% disk activity

Hello,

1.

Solution 

Fraction of work: 60% CPU, 40% disk.

 SCPU = 1/((1-f)+(f/k)) = 1/((1-0.60)+(0.60/1.4)) = 120.69% 

 SDISK= 1/((1-f)+(f/k)) = 1/((1-0.40)+(0.40/2.5)) = 131.58% 

a. Choose the CPU upgrade: $5000/120.69% = $41.43

$8000/131.58% = $38.00

 b. The disk option gives a better performance improvement. 

c. All things are equal when you pay $5451.16 for the disk upgrade.

 ______________________________________________________________

If system activity consists of 55% processor time and 45% disk activity

Fraction of work: 55% CPU, 45% disk. 

SCPU = 1/((1-f)+(f/k)) = 1/((1-0.55)+(0.55/1.4)) = 118.64% 

SDISK= 1/((1-f)+(f/k)) = 1/((1-0.45)+(0.45/2.5)) = 136.99%

Step-by-step explanation

a. Choose the CPU upgrade. This will cost $42.14 per 1% improvement versus $58.40 for the disk.

 b. The disk upgrade gives the greater improvement: 136.99% versus 118.64% for the processor. 

 c. The break-even point would be with a disk upgrade costing $5772.59.

Amdahls's Law. This law characterizes the interrelationship of the components within the system