A PC technician is sizing a power supply unit (PSU) and placing expansion cards for a high… — CompTIA A+ (Core 1 & Core 2)

A PC technician is sizing a power supply unit (PSU) and placing expansion cards for a high-performance workstation. The system components have the following peak power requirements:

- CPU: $140\text{ W}$
- Discrete Graphics Card (GPU): $280\text{ W}$
- PCIe x4 RAID Controller Card: $25\text{ W}$
- System RAM, Storage Drives, and Cooling Fans: $60\text{ W}$

The motherboard features two physical PCIe x16 expansion slots: Slot 1 is connected directly to 16 CPU lanes, while Slot 2 is wired to 4 chipset lanes. To ensure system stability and longevity, the total peak power draw must not exceed $80\%$ of the PSU's rated continuous wattage capacity.

Which of the following combinations correctly identifies the minimum standard PSU wattage rating required and the optimal expansion slot installation for the RAID controller?

650 W PSU with the RAID controller installed in Slot 2Answer
B
550 W PSU with the RAID controller installed in Slot 2
C
650 W PSU with the RAID controller installed in Slot 1
D
750 W PSU with the RAID controller installed in Slot 2

Answer

A 650 W PSU with the RAID controller installed in Slot 2 is the correct configuration.

Summing the peak power draw for all system components (

140\text{ W} + 280\text{ W} + 25\text{ W} + 60\text{ W}

) yields

505\text{ W}

. To satisfy the requirement that

505\text{ W}

represents no more than

80\%

of the PSU's continuous capacity, the minimum rating needed is

505 / 0.80 = 631.25\text{ W}

. The nearest standard rating meeting this threshold is

650\text{ W}

. Additionally, installing the PCIe x4 RAID card in Slot 2 (wired for x4 lanes) preserves Slot 1's full 16 CPU lanes for the high-demand GPU.

Step-by-Step Solution

Calculate the total peak system power demand across all components.

140\text{ W (CPU)} + 280\text{ W (GPU)} + 25\text{ W (RAID)} + 60\text{ W (Peripherals)} = 505\text{ W}

Accurate PSU sizing requires accounting for total peak draw rather than base TDP ratings.

Apply the 80% maximum utilization rule to determine minimum continuous rated capacity.

\text{Minimum Rating} = \frac{505\text{ W}}{0.80} = 631.25\text{ W}

Operating within 80% of rated capacity maintains power efficiency and prevents unexpected shutdowns during load spikes.

Select the appropriate standard PSU wattage and evaluate PCIe lane routing.

Select a

650\text{ W}

standard PSU rating. Install the x4 RAID controller into physical Slot 2 (wired for x4 chipset lanes) so physical Slot 1 (wired for x16 CPU lanes) remains allocated to the GPU.

Matching card lane requirements to physical slot wiring prevents bandwidth bottlenecks on high-throughput graphics adapters.

Key Concept

Power supply wattage sizing with safety margins and PCIe lane allocation efficiency

Estimated Time:3m 0s

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